Capillary effect based selective sealing strategy for boosting the piezoelectric MEMS speaker performance

doi:10.21203/rs.3.rs-3908146/v1

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Capillary effect based selective sealing strategy for boosting the piezoelectric MEMS speaker performance

https://doi.org/10.21203/rs.3.rs-3908146/v1

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To address the serious acoustic performance deterioration induced by the air leakage and the asynchronous vibration in the electro-acoustic transduction structures, a novel sealing strategy is proposed targeting to one of the most widely reported piezoelectric MEMS speaker designs that consists of multi cantilever beams, in which an automatic and selective filling of the liquid polydimethylsiloxane (PDMS) to the air gaps between cantilevers under the capillary effect followed by curing is developed. In the proof-of-concept demonstration, an obvious enhancement in sound pressure level (SPL) within frequency range lower than 100 Hz after sealing is experimentally demonstrated, in which the SPL is increased by 4.9 dB at 20 Hz. At the same time, the deteriorated SPL response near the resonant frequencies of the cantilever beams (17 kHz-17.5 kHz) caused by their asynchronous vibration that is induced by the fabrication process non-uniformity is also significantly improved and a boosted SPL of around 15 dB is successfully achieved. Moreover, nearly the same SPL response as the initial counterpart in the frequency band from 100 Hz to 16 kHz and even smaller total harmonic distortion (THD) of 0.728% at 1 kHz under 40 V_pp driving voltage can be obtained in the sealed devices. In comparison to the existing sealing methods, the current approach offers easy operation, low damage risk, excellent repeatability/reliability and excellent robustness advantages, and provides a promising technical solution for the MEMS acoustic devices.

Physical sciences/Engineering

Physical sciences/Physics

With the development of the Internet of Things and wearable electronic devices, there is a growing demand for low power consumption, miniaturization and intelligence mobile devices¹. Traditional electromagnetic speakers face technical challenges due to their large size, high power consumption and complex manual assembly², making it difficult for them to adapt to the wave of intelligent device development. Therefore, the MEMS speaker technology has obtained significant attention in recent years, and different types of MEMS speakers have been proposed, including electromagnetic^3,4, electrostatic^5,6 and piezoelectric ones^7–17. Among them, the piezoelectric MEMS speaker has been treated as the most promising substitute due to its relatively simple structure, high operation reliability, low power consumption and moderate performance. Till now, great progress has been achieved in this area and various piezoelectric MEMS speakers have been developed for high frequency⁷, broadband⁸ and directional emission⁹ applications. Based on the electro-acoustic transduction structure design, the piezoelectric MEMS speakers can be roughly categorized into three groups, namely fully clamped diaphragm¹⁰, partially clamped diaphragm^11–14 and cantilever beam like diaphragm^7,8,15,16, in which the cantilever beam like diaphragm design has been attracting more extensively study owing to their distinct advantages as high SPL output capability, less sensitive to the fabrication process related residual stress and large linear operation range. In most cases, the speaker usually consists of multi cantilever beams^7,8, and each of them can operate independently without any mechanical coupling. Unfortunately, the air gaps surrounding the cantilever structures can provide the air leakage pathway, causing the "acoustic short circuit" issue. Under its associated acoustic loss effect, the generated SPL from the speaker will be weakened, especially in the low-frequency band^12,13. In addition, the non-uniform size control during the fabrication can lead to inconsistency in the mechanical performance of these cantilever beams, thus changing their frequency responses. If the speaker is driven by the same control signal, a well-known asynchronous vibration phenomenon will appear between different resonant frequencies. As a result, the sound signals emitting from these cantilever beams will be cancelled out by each other, significantly decreasing the output SPL further.

In order to treat these problems, the narrower air gap and more rigorous process control can be used but at the expense of distinctly increased difficulty. Moreover, the residual stress induced initial structure deformation and the relatively large vibration amplitude during operation both can inevitably introduce additional gap widening, making the problem still remain unsolved. In fact, sealing the air gap is the most fundamental solution and great efforts have been made by researchers all over the world. In Ref ¹⁸ the whole surface of the released MEMS speaker is covered by a 15 µm thick polydimethylsiloxane (PDMS) film so as to block the air leakage, and a 15 dB SPL improvement at 20 Hz has been successfully achieved. Nevertheless, the post-release cantilever beams are relatively fragile and usually demonstrate certain warpage, which makes the reliable film coverage difficult and raises structure damage risk. A similar concept has also been used in Ref ^19–21, in which a Parylene C layer is directly deposited onto the device surface before the releasing process instead. Although the structure damage risk is largely reduced, the high Young's modulus of the Parylene C will increase the structure stiffness, thus changing the original device performance accordingly. At the same time, the special facility requirement for the film deposition also complicates the process.

To explore a better solution, a novel sealing strategy for the MEMS speaker is presented in this paper. In the current case, the liquid PDMS is used to selectively fill the air gaps between cantilevers under the capillary effect followed by curing. Considering the fact that the filling is actually a self-driven process, the implementation and the process control can be largely simplified, and high reliability and repeatability can be easily achieved. Moreover, since the capillary effect only occurs at the air gap region, highly constrained PDMS distribution can be obtained. Combining the low Young’s modulus and excellent elasticity of the cured PDMS, the sealing will introduce negligible impact on the mechanical performance of the existing speaker structure itself.

Design and theoretical analysis

The piezoelectric MEMS speaker used in the current proof-of-concept demonstration consists of six identical triangular composite cantilever beams, acting as the electro-acoustic transduction structure. These cantilever beams are constructed from a Mo(top electrode)-ScAlN(piezoelectric layer)-Mo(bottom electrode) sandwich like piezoelectric actuator structure deposited onto a silicon support layer. They are separated by air gaps and arranged into a hexagon with their fixed ends being anchored to the same SOI substrate as shown in Fig. 1a. In this design, the PDMS is used as the sealing material, and it is only applied into the air gaps between the cantilever beams, minimizing its impact on the mechanical characteristics of the structure as much as possible. The gap filling process using the "capillary effect" is also schematically illustrated in Fig. 1a. A liquid PDMS droplet is placed onto the edge of the air gap region using a syringe dispensing system. Under the influence of the surface tension, a certain amount of the liquid PDMS will be automatically drawn into the narrow air gaps. With the flow of the PDMS, effective and selective gap filling will be obtained, and this process will be self-stopped based on the liquid viscosity. It’s obvious that this sealing method is easy to perform and does not require strict control of the applied PDMS amount. Through repeating the above operation, all of the air gaps in the speaker can be sequentially filled. Afterwards, the device is put into an oven for the PDMS curing process. Detailed structure parameters used in the current proof-of-concept demonstration are also provided in the figure.

Figure 1b shows a triangular cantilever beam anchored at the base with a thickness, length and width denoted as H, L and W, respectively. Assuming that the base of the cantilever beam is at the coordinate origin, the cross-sectional width of the triangular cantilever beam gradually decreases from the base to the tip:

$$\begin{array}{c}b\left(x\right)=W\frac{L-x}{L} \left(1\right)\end{array}$$

When a uniformly distributed load force F in the z-direction is applied onto the cantilever beam surface, the resultant bending moment can be expressed as:

$$\begin{array}{c}M\left(x\right)=\overrightarrow{r}\times \overrightarrow{F}=\int F\frac{{\left(L-x\right)}^{2}}{{L}^{2}}dx=-\frac{1}{3}\frac{F}{{L}^{2}}{\left(L-x\right)}^{3} \left(2\right)\end{array}$$

where $M\left(x\right)$ represents the bending moment at the coordinate x, $\overrightarrow{r}$ is the moment arm that is perpendicular to the applied force $\overrightarrow{F}$.

For a variable cross-section triangular cantilever beam, its moment of inertia can be expressed as:

$$\begin{array}{c}I\left(x\right)=\frac{b\left(x\right){H}^{3}}{12} \left(3\right)\end{array}$$

According to the relationship between deflection and bending moment²², and considering the boundary conditions of the cantilever beam

$$\begin{array}{c}\frac{{d}^{2}w}{d{x}^{2}}=-\frac{M\left(x\right)}{EI\left(x\right)} \left(4\right)\end{array}$$

$$\begin{array}{c}\frac{dw}{dx}{|}_{x=0}=0 \left(5\right)\end{array}$$

$$\begin{array}{c}w{|}_{x=0}=0 \left(6\right)\end{array}$$

The deflection curve of the triangular beam can be determined:

$$\begin{array}{c}w\left(\stackrel{-}{x}\right)={w}_{max}\times \frac{1}{3}\left[{\left(1-\stackrel{-}{x}\right)}^{4}-4\left(1-\stackrel{-}{x}\right)+3\right] \left(7\right)\end{array}$$

$$\begin{array}{c}{w}_{max}=\frac{F{L}^{3}}{EW{H}^{3}} \left(8\right)\end{array}$$

where $w\left(\stackrel{-}{x}\right)$ represents the deflection of the triangular beam, $\stackrel{-}{x}$ is the normalized position, ${w}_{max}$ is the deflection at the tip of the beam, and E is the Young's modulus of the beam.

The first-order resonant frequency of the triangular beam is given by²³:

$$\begin{array}{c}{f}_{tri}=0.3295\frac{H}{{L}^{2}}\sqrt{\frac{E}{\rho }} \left(9\right)\end{array}$$

From Eq. (9), it can be seen that the resonant frequency of the triangular cantilever beam structure is inversely proportional to the square of its length. Figure 1c illustrates the relationship between the resonant frequency of the cantilever beam and its length. Considering the currently adopted cantilever design with 1500 µm width and approximately 1299 µm length, it is evident that the resonant frequency of the cantilever beams is sensitive to its length, where a variation of 50µm in length results in a frequency shift of 1.44 kHz. This implies that any non-uniformity in the back cavity etching during the manufacturing process can easily lead to different lengths in the six cantilever beams, resulting in an inconsistency in their resonant frequencies. Considering the fact that a well-known phase reversal characteristic will occur for a structure operating around its resonant frequency, when all of the cantilever beams are driven with the same control signal, the discrepancy in the resonant frequency will induce asynchronous vibration between them. As a result, the sound signals generated by these cantilever beams will be cancelled out by each other, introducing a remarkable dip in the SPL frequency spectrum⁷.

Numerical simulation

A simulation model of the proposed piezoelectric MEMS speaker within a simplified ear canal environment is established in COMSOL as depicted in Fig. 2a. In simulation, a 1/4 symmetric model is employed to simplify the model, reduce the computational burden in 3D finite element simulations and ease memory demands. The MEMS speaker is represented by considering only two layers including the piezoelectric layer and the support layer. A "fixed constraint" boundary condition is applied at the base of the cantilever beams.

To emulate the ear canal, a particularly designed cylindrical structure with similar acoustic characteristics is used. The lateral and end sides of this "simplified ear canal" are set as acoustic impedance boundaries that match those of the human ear canal. To account for the frictional losses caused by air within the gaps and to accurately estimate the acoustic losses from both sides of the cantilever beam through the gaps, the air gaps and their adjacent regions (cylindrical domain) are defined as the "thermo-viscous acoustic" domain. Based on the model described above, transient simulation is conducted to calculate the sound pressure distribution on both sides of the cantilever beam as illustrated in Fig. 2b. For clarity, the figure retains only one cantilever and one air gap, displaying results from the thermo-viscous acoustic domain near the air gap. It can be observed that when the cantilever is driven to vibrate, opposite sound pressures will be excited on its front and back sides, and they are connected through the air gap, resulting in acoustic short-circuit phenomena and inducing acoustic loss.

The generated SPL at 20 Hz under 40 V_pp driving voltage by the proposed speaker before sealing as a function of the air gap width is studied as shown in Fig. 2c. It can be seen that the acoustic loss induced SPL reduction is negligible for the air gap width less than 5 µm as reported by others¹⁴. After that, with the increasing air gap, the decrease of the SPL will become distinct. Referring to the following experiment result, the air gap width will be increased from the initially designed 5 µm to 6.8 µm due to the effect of the chlorine based dry etching process for ScAlN. As a result, a nearly 1.82 dB drop of the SPL will be caused. At the same time, since the residual stress as well as the stress gradient that present in the deposited composite stacking layers will deform the cantilever beam, thus widening the air gap further especially around the tip region. Therefore, its effect on the device performance is also studied. Figure 2d shows the changes of the air gap between the cantilever tips and the corresponding SPL at 20 Hz under different residual stresses. It can be seen that with the increase of the residual stress, the air gap will become wider and wider, followed by a monotonous decrease in SPL. Considering a residual stress of 320 MPa in the as-deposited stacking layer, the tip air gap will be increased from 6.8 µm to 8.2 µm, under the effect of which additional SPL reduction of nearly 0.65 dB will be resulted.

The generated SPL frequency responses in the audio range from 20 Hz to 20 kHz from the speaker before and after sealing treatment with PDMS are also studied as shown in Fig. 3a. For clarification, the SPL curve from 20Hz to 100Hz is magnified and presented as an inset. It’s obvious that the SPL in the low-frequency range can be improved after sealing, in which a 2.82 dB SPL enhancement at 20 Hz operation frequency can be achieved. In contrast, the SPL response in the mid and high-frequency nearly remains unchanged, and this is mainly attributed to the lower material strength of the PDMS as well as its selective sealing.

Moreover, the issue induced by the inconsistent mechanical characteristics of the cantilever beams due to the fabrication process is also studied. Figure 3c shows the resonant vibration mode of the speaker at 19 kHz in the ideal case that all of the cantilever beams are the same, from which the synchronized vibration can be observed. To simulate the process induced dimension change, four of the cantilever beams are intentionally designed to be 20 µm longer than the other two. In this case, the speaker will demonstrate two closely spaced resonant frequencies instead, namely 18.45 kHz and 19 kHz. When all of the cantilever beams are driven using the same control signal of 40 V_pp with its frequency falling between these two resonant frequencies, a distinct asynchronous vibration between the cantilever beams will occur as shown in Fig. 3d, thus inducing a significant dip more than 20 dB in the SPL response (see Fig. 3b). After sealing the air gap with PDMS, all of the cantilever beams will be mechanically coupled together as a new combination with resonant frequency of 18.9 kHz, forcing them into synchronous vibration as shown in Fig. 3e. As a result, the above-mentioned SPL drop issue can be totally eliminated. Furthermore, the sealing treatment only leads to a slight decrease of 0.1 kHz (0.5%) in the resonant frequency of the speaker, indicating that the proposed sealing method has little impact on the mechanical performance of the existing speaker structure.

To assess the operation reliability of the speaker after sealing, the stress distribution in the speaker driven at the resonant frequency with 40 V_pp is extracted as shown in Fig. 4. Due to the vibration amplification effect by resonance, the tip deflection of the cantilever beams will reach maximum, causing the highest internal stress of 103 MPa and 19.4 MPa in the cantilever beams and the PDMS, respectively. Both of these stresses are far below the safety limit, ensuring reliable operation.

Fabrication

The fabrication process of the proposed MEMS speaker is illustrated in Fig. 5a. The process starts with an 8-inch SOI (Silicon-On-Insulator) wafer including a 10 µm thick Si (Silicon) device layer and a 0.5 µm thick buried oxide layer. Initially, a series of depositions are carried out on the SOI wafer using magnetron sputtering method, involving 0.2 µm of bottom electrode Mo (Molybdenum), 1 µm of piezoelectric ScAlN (Scandium-doped Aluminum Nitride, with a Sc content of 9.6%) and an additional 0.2 µm of top electrode Mo. Subsequently, dry etching is employed to pattern the top electrode layer. Following this, the patterning of the piezoelectric layer, the growth of the passivation layer, and the via opening to the top and bottom electrodes are performed. The next step involves the fabrication of patterned Al (Aluminum) electrodes with 1 µm thickness using a lift-off process, which connect to the top and bottom electrodes of the speaker. Then, both the bottom electrode and the Si device layer are selectively etched to form the cantilever beams as well as the air gaps. Finally, deep silicon etching for the back cavity and the release of the buried oxide layer are performed. After dicing, individual speaker devices are obtained.

The morphology of the as-fabricated speaker is characterized using an optical microscope and a white-light interferometer (Zygo-NewView 7300, U.S.A) as shown in Fig. 5. The air gap width around the clamped region in the device is measured to be 6.8 µm. From the measurement result of the speaker's three-dimensional contour, the upward bending of the cantilever beams is clearly visible and their tip deflection is obtained as 42.14 µm, indicating the presence of significant residual tensile stress of around 320 MPa in the as-deposited stack layer.

A speaker gap sealing operation platform is constructed using a three-axis displacement stage and a microscope as shown in Fig. 6. First, the liquid PDMS prepolymer (mixture of the PDMS base and the curing agent with a weight ratio of 10:1) is prepared and loaded into a syringe. The syringe is then clamped onto the three-axis displacement stage, allowing precise positioning under the assistance of the microscope. Finally, a dispenser (MUSASHI-SUPER ΣCMII V5, Japan) is used to place the liquid PDMS droplet at the edge region of the air gap.

In the experiment, a syringe equipped with a 34G needle is used, and the volume of the dispensed liquid PDMS is controlled by adjusting the air pressure and the dispensing time to prevent excessive PDMS from spreading onto undesired cantilever regions. Although PDMS has high transmittance for visible light (> 93%), it still can be observed under the microscope. Figure 6 demonstrates the partial sealing result, where the liquid PDMS is visible as a dark yellow color in the gap region and the unsealed gaps remain black. During operation, the PDMS flow along the air gap from its edge to center under the action of the capillary effect can be clearly observed. When all of the air gaps are sealed, the device is placed in an oven to cure the filled liquid PDMS.

Before and after the air gaps sealing, various measurements are conducted to evaluate the electrical, mechanical and acoustic characteristics of the speaker. Firstly, the capacitance and loss factor frequency spectrum of the device are measured using an LCR meter (Agilent-E4980A, USA) as depicted in Fig. 7. Before PDMS sealing, the capacitance and the loss factor curves of the speaker present distinct fluctuations in the frequency range from 17 kHz to 19 kHz (see Fig. 7a), which are thought to be mainly caused by the inconsistent resonance frequencies between the cantilever beams. The inset of Fig. 7a also provides the measured mode shapes of the speaker by a laser Doppler vibrometer (Polytec-MSA 600, Germany), from which the asynchronous vibration between the cantilever beams can be clearly observed, further confirming the existence of the resonance frequency discrepancy. In comparison, after sealing treatment, both the capacitance and the loss factor curves will demonstrate regular change tendency. This indicates that all of the cantilever beams are currently in synchronous working mode, which can also be supported by the laser Doppler velocimetry measurement results provided in Fig. 7b inset, thus validating the sealing effectiveness as simulation expectation.

The SPL frequency spectrum of the as-fabricated piezoelectric MEMS speaker is characterized in an IEC ear simulator (B&K-4195, Denmark), and the results are shown in Fig. 8. During the measurement, the speaker is excited by a 40 V_pp driving signal. Following the PDMS sealing for the air gaps, there is an obvious SPL improvement in the frequency range lower than 100 Hz, and a 4.9 dB enhancement at 20 Hz can be obtained, which is attributed to the prevention of the acoustic short circuit by the sealing treatment. In addition, in the initial status before sealing, the SPL frequency spectrum of the speaker displays a distinct amplitude dip between 17 kHz and 17.5 kHz. This is a result of the asynchronous vibration between the cantilever beams that leads to the mutual cancellation of sound signals, agreeing well with the simulation results. In comparison, after sealing, the asynchronous vibration issue can be well solved and all of the cantilever beams will be forced to vibrate in synchronous mode as a whole combination structure. As a result, significant SPL enhancement as high as 15 dB in the dip region can be achieved. At the same time, the SPL response in the frequency range from 100 Hz to 16 kHz nearly remains constant after sealing as expected, and negligible change in the acoustic characteristics of the sealed speaker can be found after extended operation, demonstrating excellent robustness of the sealing method. Moreover, the total harmonic distortion (THD) at 1 kHz for the speaker before and after sealing treatment is measured to be 0.816% and 0.728%, respectively, further representing good performance.

In the existing piezoelectric MEMS speaker technology, the cantilever beam like diaphragm design has been attracting more extensive study owing to their distinct advantages as high SPL output capability, less sensitivity to the fabrication process related residual stress and large linear operation range. However, the inevitable air leakage associated with the air gap in the structure will lead to noticeable SPL decrease in the low frequency range. In addition, the asynchronous vibration phenomenon, which is caused by the process induced inconsistencies in the mechanical performance between multi cantilever beams, will significantly deteriorate the SPL near the resonance frequency further.

In this work, the air leakage and the asynchronous vibration phenomena of the proposed piezoelectric MEMS speaker are validated through modeling and experimental measurement. FEM simulation reveals that the SPL of the MEMS speaker decreases with the increase of the air gap width. Due to the initial deformation of the cantilever beams caused by the residual stress, the air gap will be widened further especially around the tip region, leading to an additional decrease in SPL. Moreover, the asynchronous vibration occurs near the resonance frequencies when the six cantilever beams are not perfectly matched, causing significant reduction in SPL.

To treat these problems, a novel sealing strategy based on the capillary effect is proposed. Both simulation results and experimental measurements confirm the suppression of the air leakage and the asynchronous vibration after PDMS sealing. The LCR measurement results indicate that there are multiple discrete resonance peaks in the prepared piezoelectric MEMS speaker, which merge into a single one after the sealing operation. Acoustic measurement is conducted using a 711 human ear simulator, the results of which indicate that the SPL is increased by 4.9 dB at 20 Hz after sealing, and a boosted SPL of around 15 dB is successfully achieved near the resonant frequency of the cantilever beams. Furthermore, the proposed sealing approach offers advantages including convenient operation, precise control and minimal impact on mechanical characteristics. Notably, this strategy is also applicable to other air-coupled MEMS acoustic devices that featuring air gap structures and encountering air leakage issues, such as MEMS microphones and PMUTs.

In the future, with the optimization of the piezoelectric MEMS speaker design, the SPL in the low frequency range is expected to be improved further, and some microfluidic structures can also be involved into the device design, making the proposed sealing strategy more precise and easier to operate.

Conflict of interest

The authors declare no competing interests.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (NSFC) (12174137); National Key Research and Development Plan of China (2020YFB2008800); Innovation Project of Optics Valley Laboratory (Grant No. OVL2023ZD003).

Wang, H. et al. Review of Recent Development of MEMS Speakers. Micromachines 12, 1257 (2021).
Shahosseini, I. et al. Optimization and Microfabrication of High Performance Silicon-Based MEMS Microspeaker. IEEE Sens. J. 13, 273–284 (2013).
Setiarini, A. et al. A Novel Structure of Electromagnetic MEMS Speaker for Hearing Aid Application. in 2018 International Conference on Radar, Antenna, Microwave, Electronics, and Telecommunications (ICRAMET) 112–116 (IEEE, 2018).
Shahosseini, I. et al. Electromagnetic MEMS microspeaker for portable electronic devices. Microsyst. Technol. 19, 879–886 (2013).
Kaiser, B. et al. Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers. Microsyst. Nanoeng. 5, 1–11 (2019).
Roberts, R. C. et al. Electrostatically Driven Touch-Mode Poly-SiC Microspeaker. in 2007 IEEE Sensors 284–287 (IEEE, 2007).
Chen, Y.-C. et al. On the design of a two-way piezoelectric MEMS microspeaker based on a multi-shape cantilever array for high-frequency applications. J. Micromech. Microeng. 33, 074001 (2023).
Sun, M., Zhang, M., Liu, C. & Pang, W. Broadband MEMS Speaker by Single-Way Multi-Resonance Array with Acoustic Damping Tuning: A Proof of Concept. in 2023 IEEE 36th International Conference on Micro Electro Mechanical Systems (MEMS) 677–680 (IEEE, 2023).
Shao, Z., Pala, S., Liang, Y., Peng, Y. & Lin, L. A Single Chip Directional Loudspeaker Based on PMUTS. in 2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS) 895–898 (IEEE, 2021).
Wang, H., Feng, P. X.-L. & Xie, H. A Dual-Electrode MEMS Speaker Based on Ceramic PZT with Improved Sound Pressure Level by Phase Tuning. in 2021 IEEE 34th International Conference on Micro Electro Mechanical Systems (MEMS) 701–704 (IEEE, 2021).
Wang, Q. et al. A Piezoelectric MEMS Speaker with a Combined Function of a Silent Alarm. Micromachines 14, 702 (2023).
Cheng, H.-H. et al. Monolithic Integration of PZT Actuation Units of Various Activated Resonances for Full-Range MEMS Speaker Array. in 2023 IEEE 36th International Conference on Micro Electro Mechanical Systems (MEMS) 685–688 (IEEE, 2023).
Gazzola, C., Zega, V., Cerini, F., Adorno, S. & Corigliano, A. On the Design and Modeling of a Full-Range Piezoelectric MEMS Loudspeaker for In-Ear Applications. J. Microelectromech. Syst. 1–12 (2023).
Stoppel, F. et al. Novel membrane-less two-way MEMS loudspeaker based on piezoelectric dual-concentric actuators. in 2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS) 2047–2050 (IEEE, 2017).
Yuan, N.-H., Chen, C.-C., Fuh, Y.-K. & Li, T. T. Acoustic Performance of Stress Gradient-Induced Deflection of Triangular Unimorphic/Bimorphic Cantilevers for MEMS Applications. Materials 16, 2129 (2023).
Fawzy, A. Membraneless Piezoelectric MEMS speakers based on AlN Thin Film. JES J. Eng. Sci. 50, 1–8 (2022).
Liechti, R. et al. High performance piezoelectric MEMS loudspeaker based on an innovative wafer bonding process. Sens. Actuator A-Phys. 358, 114413 (2023).
Xu, L. et al. A Piezoelectric MEMS Speaker with Stretchable Film Sealing. in 2023 IEEE 36th International Conference on Micro Electro Mechanical Systems (MEMS) 673–676 (IEEE, 2023).
Ma, Y. et al. A PZT MEMS loudspeaker with a quasi-closed diaphragm. Sens. Actuator A-Phys. 358, 114454 (2023).
Wang, Q. et al. Obtaining High SPL Piezoelectric MEMS Speaker via a Rigid-Flexible Vibration Coupling Mechanism. J. Microelectromech. Syst. 30, 725–732 (2021).
CHO, I.-J., JANG, S. & NAM, H.-J. A Piezoelectrically Actuated MEMS Speaker with Polyimide Membrane and Thin Film Pb(Zr,Ti)O3(PZT) Actuator. Integr. Ferroelectr. 105, 27–36 (2009).
Ventsel, E. & Krauthammer, T. Thin plates and shells: theory, analysis, and applications. (Dekker, 2001).
Kai Yang, Zhigang Li, Yupeng Jing, Dapeng Chen, & Tianchun Ye. Research on the resonant frequency formula of V-shaped cantilevers. in 2009 4th IEEE International Conference on Nano/Micro Engineered and Molecular Systems 59–62 (IEEE, 2009).

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Capillary effect based selective sealing strategy for boosting the piezoelectric MEMS speaker performance

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Abstract

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Introduction

Materials and method

Design and theoretical analysis

Numerical simulation

Fabrication

Results

Discussion and conclusion

Declarations

Conflict of interest

Acknowledgements

References

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